SUPPLEMENTS
Which Supplements Are Actually Worth Taking?
The UK supplement industry is worth over £500 million a year. Most of that money is wasted. A 2019 BMJ meta-analysis of 277 randomised trials found that the vast majority of vitamin and mineral supplements had no measurable effect on cardiovascular outcomes or mortality in the general population. The exceptions were notable — and they're the ones worth your attention.
The problem isn't supplements themselves. It's that most people take them blindly. They buy what Instagram recommends, stack five things they don't need, and skip the one thing they actually do. A blood test changes the equation entirely — it tells you what's low, what's fine, and where your money is genuinely worth spending.
This guide covers the supplements with the strongest evidence behind them, who actually needs each one, and how to know whether you're one of them — without guessing.
By Helvy · Medically reviewed
Published 2026-04-07 · 2,400 words · 10 min read
The one rule that saves you money
If you don't have a deficiency, you almost certainly don't need a supplement. That's not a health-guru opinion — it's the NHS position, the British Dietetic Association position, and the conclusion of virtually every large-scale meta-analysis published in the last decade.
The caveat: many people do have deficiencies and don't know it. The National Diet and Nutrition Survey consistently shows that significant portions of the UK population fall short on vitamin D, iron, magnesium, selenium, and omega-3 fatty acids. You won't feel a deficiency until it's pronounced. By then, you've been running suboptimally for months or years.
The answer isn't to take everything just in case. It's to test first, supplement second. A comprehensive blood test tells you exactly which nutrients are low and which are fine — so you spend money only on what your body actually needs.
Tier 1: Strong evidence — most people benefit
These supplements have robust evidence from large randomised controlled trials and systematic reviews. In the UK specifically, population-level data supports supplementation for a significant proportion of adults.
Vitamin D →
Essential for mostTHE EVIDENCE
The UK government recommends that everyone considers taking 10 micrograms (400 IU) of vitamin D daily during autumn and winter. NICE guidelines (CKS, updated 2024) confirm that vitamin D deficiency is widespread in the UK due to limited sunlight and indoor lifestyles. A 2022 Lancet Diabetes & Endocrinology meta-analysis of 44 RCTs found significant reductions in autoimmune disease incidence with vitamin D supplementation.
WHO NEEDS IT
Almost everyone in the UK from October to March. Year-round for people with darker skin, those who cover most of their skin outdoors, shift workers, office workers, and anyone north of Birmingham (which is most of the country). If your blood level is below 50 nmol/L, you're deficient. Below 75 nmol/L is suboptimal for performance.
TYPICAL DOSE
10 mcg (400 IU) daily as a minimum. If blood tests show deficiency, 1,000–4,000 IU daily is common under clinical guidance. Vitamin D3 (cholecalciferol) is better absorbed than D2.
THE CAVEAT
Vitamin D is fat-soluble — it accumulates. Don't mega-dose without testing. Levels above 150 nmol/L can cause hypercalcaemia. Test, dose appropriately, retest in 3 months.
Omega-3 (EPA & DHA) →
Strong evidenceTHE EVIDENCE
The VITAL trial (2019, NEJM) found a 28% reduction in heart attacks with omega-3 supplementation. A 2020 BMJ meta-analysis of 86 RCTs confirmed benefits for cardiovascular mortality, particularly at doses above 1g EPA+DHA daily. The REDUCE-IT trial showed a 25% reduction in cardiovascular events with high-dose EPA. The British Heart Foundation acknowledges omega-3's role in heart health.
WHO NEEDS IT
Anyone who eats fewer than two portions of oily fish per week — which is the majority of UK adults. Particularly important for cardiovascular health, brain function, and managing inflammation. Your omega-3 index (measured via blood test) should ideally be above 8%; most UK adults sit between 4–6%.
TYPICAL DOSE
1,000–2,000 mg combined EPA+DHA daily. Look for supplements that list EPA and DHA separately on the label — many '1,000mg fish oil' capsules contain only 300mg of actual EPA+DHA.
THE CAVEAT
Quality varies enormously. Choose supplements tested for heavy metals and oxidation (look for IFOS certification). Algae-based omega-3 is the plant-based alternative with equivalent bioavailability for DHA.
Magnesium →
Widely deficientTHE EVIDENCE
The National Diet and Nutrition Survey shows that a significant proportion of UK adults don't meet the reference nutrient intake for magnesium. A 2017 BMJ Open meta-analysis found that magnesium supplementation reduced blood pressure in hypertensive individuals. A 2022 Nutrients systematic review linked adequate magnesium to improved sleep quality, reduced anxiety, and better exercise recovery.
WHO NEEDS IT
Athletes and active people (magnesium is lost through sweat), anyone with poor sleep, people under chronic stress, heavy alcohol consumers, and those on proton pump inhibitors (PPIs). Standard serum magnesium blood tests catch only severe deficiency — red blood cell magnesium is more sensitive.
TYPICAL DOSE
200–400 mg daily. Magnesium glycinate or bisglycinate for sleep and anxiety. Magnesium citrate for general use. Magnesium threonate for cognitive function. Avoid magnesium oxide — it has poor bioavailability and mainly acts as a laxative.
THE CAVEAT
Magnesium can interact with antibiotics, bisphosphonates, and some blood pressure medications. Space doses 2 hours apart from other medications. High doses (above 400mg) can cause loose stools.
Tier 2: Good evidence — if your blood shows a need
These supplements have solid evidence for people with documented deficiencies or specific risk factors. The key word is if — supplementing when your levels are already adequate is a waste of money and may carry risks.
Vitamin B12 →
Test firstTHE EVIDENCE
B12 deficiency is well-established as a cause of megaloblastic anaemia, peripheral neuropathy, and cognitive impairment. NICE clinical knowledge summaries confirm that deficiency is common in vegans, vegetarians, older adults (reduced intrinsic factor), and people on metformin or PPIs. The BMJ Best Practice guidelines recommend testing B12 in anyone presenting with fatigue, paraesthesia, or cognitive symptoms.
WHO NEEDS IT
Vegans and vegetarians (B12 is found almost exclusively in animal products), adults over 50 (absorption decreases with age), anyone on metformin or long-term PPI use, and people with coeliac disease or Crohn's. If your blood level is below 200 ng/L, supplementation is indicated.
TYPICAL DOSE
Oral: 1,000 mcg methylcobalamin daily for deficiency, 10–25 mcg daily for maintenance. Sublingual forms may improve absorption. Severe deficiency may require intramuscular injections (prescribed by your GP).
THE CAVEAT
Cyanocobalamin is cheaper but requires conversion by the body. Methylcobalamin is the active form. Very high serum B12 without supplementation can occasionally indicate liver disease — always interpret results with a clinician.
Iron →
Test firstTHE EVIDENCE
Iron deficiency is the most common nutritional deficiency worldwide. The WHO estimates that 25% of the global population is anaemic, with iron deficiency being the leading cause. In the UK, the NDNS shows that 27% of women aged 19–64 have iron intakes below the lower reference nutrient intake. NICE recommends checking ferritin in anyone with unexplained fatigue.
WHO NEEDS IT
Women with heavy periods (the most common cause in the UK), endurance athletes (foot-strike haemolysis and increased hepcidin), vegetarians and vegans (non-haem iron is less bioavailable), frequent blood donors, and people with coeliac disease. Your ferritin should ideally be above 30 mcg/L — below 15 mcg/L is definitive deficiency.
TYPICAL DOSE
If deficient: 65–200 mg elemental iron daily, taken with vitamin C to enhance absorption. Ferrous bisglycinate causes fewer GI side effects than ferrous sulphate. Take on an empty stomach if tolerated, or with a small meal if not.
THE CAVEAT
Never supplement iron without testing. Excess iron is toxic and can cause organ damage. Haemochromatosis (hereditary iron overload) affects roughly 1 in 200 people of Northern European descent. Always retest ferritin 8–12 weeks after starting supplementation.
Vitamin B6 →
Targeted useTHE EVIDENCE
B6 is a cofactor in over 100 enzyme reactions including neurotransmitter synthesis, haemoglobin production, and homocysteine metabolism. The NDNS shows marginal intakes in some UK population groups. A 2022 Human Psychopharmacology study found that high-dose B6 (100mg/day) reduced self-reported anxiety in young adults by modulating GABA activity.
WHO NEEDS IT
People with elevated homocysteine (B6 helps convert homocysteine to cysteine), those on hormonal contraceptives (which can deplete B6), heavy alcohol consumers, and people with autoimmune conditions. A blood test can confirm whether your levels warrant supplementation.
TYPICAL DOSE
10–50 mg daily for general support. Higher doses (up to 100 mg) under clinical supervision for specific indications. The UK tolerable upper intake is 200 mg/day.
THE CAVEAT
Long-term high-dose B6 (above 200 mg/day) can cause peripheral neuropathy — the very symptom it's sometimes taken to prevent. Always use the lowest effective dose.
Zinc →
Targeted useTHE EVIDENCE
Zinc is essential for immune function, testosterone production, wound healing, and taste/smell. A 2021 Advances in Nutrition systematic review confirmed zinc supplementation reduces the duration of common colds by approximately 2 days. The NDNS identifies suboptimal zinc intake in UK adults, particularly those on plant-based diets.
WHO NEEDS IT
Vegetarians and vegans (phytates in grains and legumes reduce zinc absorption), athletes (zinc is lost in sweat), men concerned about testosterone levels, older adults, and people with GI conditions affecting absorption.
TYPICAL DOSE
15–30 mg zinc picolinate or zinc bisglycinate daily. Take with food to reduce nausea. Avoid zinc oxide (poor absorption).
THE CAVEAT
Long-term zinc supplementation above 40 mg/day can deplete copper. If supplementing zinc regularly, consider adding 1–2 mg copper. Zinc and iron compete for absorption — space them at least 2 hours apart.
Folate →
Specific groupsTHE EVIDENCE
Folate (vitamin B9) is critical for DNA synthesis and cell division. The NHS recommends 400 mcg folic acid daily for women trying to conceive and during the first 12 weeks of pregnancy to prevent neural tube defects. NICE also recommends folate testing alongside B12 in investigation of anaemia.
WHO NEEDS IT
Women planning pregnancy or in early pregnancy (mandatory recommendation), people with elevated homocysteine, those on methotrexate or certain anti-epileptic drugs, heavy alcohol consumers, and anyone with coeliac disease or inflammatory bowel disease.
TYPICAL DOSE
400 mcg daily for general use and pregnancy planning. Methylfolate (5-MTHF) is the bioactive form and may be preferable for people with MTHFR gene variants who have difficulty converting folic acid.
THE CAVEAT
High-dose folic acid can mask B12 deficiency by correcting the anaemia while neurological damage continues. Always check B12 status alongside folate.
Tier 3: Emerging evidence — worth watching
These supplements have promising research but the evidence isn't yet strong enough to recommend universally. They may be worth considering in specific contexts — but approach with appropriate scepticism.
Creatine monohydrate
PromisingOne of the most studied sports supplements in existence, with strong evidence for strength and power output. Emerging research in the journal Experimental Gerontology suggests cognitive benefits, particularly under sleep deprivation or stress. Dose: 3–5g daily. No loading phase necessary. Safe long-term. Not measurable via standard blood test, but relevant for active individuals.
Vitamin K2 (MK-7)
PromisingK2 directs calcium into bones and away from arteries. Often paired with vitamin D supplementation. A 2019 BMJ study found that K2 (MK-7) supplementation slowed age-related arterial stiffening. Most relevant for people supplementing vitamin D long-term, post-menopausal women, and those with cardiovascular risk factors. Dose: 100–200 mcg MK-7 daily.
Ashwagandha (KSM-66)
EmergingAn adaptogen with a growing body of RCT evidence. A 2019 Medicine systematic review found significant reductions in cortisol and perceived stress. A 2022 Health Science Reports study found improvements in sleep quality. Relevance to blood testing: may modestly reduce cortisol levels and improve thyroid function (TSH). Dose: 300–600 mg KSM-66 extract daily. Not recommended during pregnancy or for people with autoimmune thyroid conditions.
Supplements most people can skip
These are commonly purchased supplements where the evidence for healthy adults without deficiencies is weak, absent, or contradicted by the research.
Multivitamins
A 2022 Lancet systematic review of 84 studies found no consistent benefit for cardiovascular disease, cancer, or all-cause mortality in the general population. If you eat a reasonably varied diet, a multivitamin is nutritional insurance you don't need — and it may give you a false sense of security while missing the one thing you're actually deficient in.
Vitamin C (for healthy adults)
Unless you have scurvy (extremely rare in the UK), supplemental vitamin C has not been shown to prevent colds, boost immunity, or improve health outcomes in well-nourished adults. A Cochrane review of 29 RCTs found no benefit for cold prevention. Most UK adults get adequate vitamin C from diet.
Biotin (for hair and nails)
Despite aggressive marketing, a 2017 Journal of Drugs in Dermatology review found insufficient evidence that biotin supplements improve hair or nail health in people without biotin deficiency (which is rare). Importantly, biotin supplementation can interfere with blood test results — falsely elevating thyroid hormone and troponin readings.
Collagen powders
Oral collagen is broken down into amino acids during digestion. While some small studies show modest improvements in skin hydration, the evidence base is limited and the studies are often industry-funded. Your body makes its own collagen if it has adequate vitamin C, zinc, and protein.
BCAAs (branched-chain amino acids)
If you eat adequate protein (1.6–2.2g per kg bodyweight for active people), BCAAs offer no additional benefit. A 2017 Journal of the International Society of Sports Nutrition review concluded that BCAAs alone do not stimulate muscle protein synthesis optimally — you need all essential amino acids, which whole protein provides.
How a blood test changes everything
The difference between effective supplementation and expensive urine is information. A comprehensive blood test measures the biomarkers that correspond directly to the supplements above:
25-OH Vitamin D
Whether you need vitamin D
Omega-3 Index
Whether you need omega-3
RBC Magnesium
Whether you need magnesium
Serum B12
Whether you need B12
Ferritin
Whether you need iron
Serum Folate
Whether you need folate
Zinc (serum)
Whether you need zinc
hs-CRP
Inflammation — guides omega-3 priority
Instead of taking seven supplements because a podcast said so, you take three because your blood said so. You save money. You avoid unnecessary interactions. And in three months, you retest to prove it worked.
That's the Helvy approach: test, understand, supplement only what you need, then verify. No guessing. No stacking for the sake of stacking. Just the things your body actually asked for.
How to build a supplement stack that actually works
1. Test first. Get a comprehensive blood panel that covers vitamins, minerals, inflammation, and hormones. This is your baseline.
2. Address deficiencies only. If your vitamin D is 35 nmol/L, supplement vitamin D. If your ferritin is 12 mcg/L, supplement iron. If everything is optimal, save your money.
3. Choose quality forms. Magnesium glycinate over oxide. Methylcobalamin over cyanocobalamin. Vitamin D3 over D2. Ferrous bisglycinate over ferrous sulphate. The form matters more than the brand.
4. Watch for interactions. Iron and zinc compete for absorption — take them at different times. Vitamin D needs adequate magnesium for conversion. Calcium blocks iron absorption. Vitamin C enhances iron absorption. Timing and pairing matter.
5. Retest in 3 months. Supplementation without follow-up is a guess that never gets checked. A retest confirms whether your levels have normalised, whether you need to adjust doses, or whether you can stop altogether.
Frequently asked questions
Should I take supplements on an empty stomach or with food?
Fat-soluble vitamins (D, K2, omega-3) should be taken with a meal containing fat for optimal absorption. Water-soluble vitamins (B12, folate, vitamin C) can be taken any time. Iron is best absorbed on an empty stomach but can be taken with a small meal if it causes nausea. Magnesium is fine with or without food.
Can I get everything I need from food alone?
In theory, yes — with a well-planned, varied diet. In practice, UK sunlight levels make vitamin D supplementation necessary for most people in winter. If you eat two portions of oily fish per week, don't need iron, and have good gut absorption, you may not need anything else. A blood test is the only way to know for certain.
Are expensive supplements better than cheap ones?
Not necessarily, but form matters. Cheap magnesium oxide is poorly absorbed compared to magnesium glycinate. Cheap fish oil may be oxidised. Look for third-party testing (IFOS for fish oil, NSF or Informed Sport for general supplements) rather than trusting price as a proxy for quality.
How long before supplements start working?
Vitamin D: 8–12 weeks to normalise levels. Iron: 8–12 weeks to replenish ferritin. B12: 4–8 weeks for symptoms to improve. Magnesium: 1–4 weeks for sleep and muscle effects. Omega-3: 8–12 weeks for omega-3 index to shift. A follow-up blood test at 3 months captures all of these.
Should I stop supplements before a blood test?
Don't stop your regular supplements before testing — the test should reflect your current status. The one exception is biotin: high-dose biotin supplements can interfere with immunoassay-based blood tests (including thyroid and troponin), so stop biotin 48–72 hours before a blood draw.
What about supplements for testosterone?
No supplement has been shown to meaningfully increase testosterone in men with normal levels. Zinc and vitamin D deficiency can suppress testosterone, so correcting those deficiencies may help — but that's treating the deficiency, not 'boosting' testosterone. If you suspect low testosterone, get a blood test for total testosterone, free testosterone, and SHBG. Read our guide on testosterone levels by age for more context.
STOP GUESSING
Find out which supplements you actually need.
A Helvy blood test measures 50+ biomarkers including every vitamin and mineral above. Results in 5 days, reviewed by a GMC-registered doctor, with personalised supplement recommendations.
Order your testMedical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional before starting any new supplement, especially if you are pregnant, breastfeeding, taking medication, or have a pre-existing medical condition. Supplements should not replace a varied, balanced diet.